Transition metal complexes bearing nitrogen containing N-heterocyclic carbene (NHC) ligands or phosphine ligands have been widely studied for use in catalysis, medicinal and materials chemistry.
The luminescent properties of transition metal complexes of palladium(0) or platinum(0) bearing NHC, or NHC and phosphorus, ligands have not been studied extensively. In contrast the luminescent properties of Cu(I), Ir(III), Pt(II) and Au(I) complexes have been subject to consideration for use in light-emitting devices such as organic light emitting diodes (OLEDs) or for sensing applications such as sensing oxygen.
Some studies have been carried out on Pd(0) and Pt(0) tetra-coordinate complexes using bidentate aryl phosphine ligands (Inorg. Chem. 2008, 47, p481-486; Tsubomura et al). Palladium (0) complexes having two or three monodentate phosphine ligands coordinating to the metal have been studied (Inorganic Chemistry Communications 2012, 20, p27-29; Ohkubo et al). Relatively weak and very weak luminescence was found for the examples studied (in solution), respectively.
More recently some examples of two coordinate palladium (0) complexes bearing an NHC and a triaryl phosphine ligand have been studied (Inorganic Chemistry Communications 2013, 35, p110-112; Tsubomura et al). A low photoluminescence quantum yield (1.4%) emission was observed for the only complex measured in that study in toluene solution.
There remains the need to find new materials for light emitting devices and sensors.